1. Field of the Invention
The present invention relates to a high-frequency coaxial resonator, which comprises a tubular dielectric member having a through hole and inner and outer conductors provided on inner and outer peripheral surfaces of the tubular dielectric member.
2. Description of the Background Art
FIGS. 9 and 10 illustrate the structures of conventional high-frequency coaxial resonators of the aforementioned type. A high-frequency coaxial resonator 30 shown in FIG. 9 comprises a tubular dielectric member 32 having a through hole 31 and inner and outer conductors 33 and 34 which are provided on inner and outer peripheral surfaces of the tubular dielectric member 32, respectively. The inner and outer conductors 33 and 34 are short-circuited by an end conductor 35 which is formed on one end surface of the high-frequency coaxial resonator 30 so as to define a high-frequency coaxial resonator of a quarter wavelength type.
Alternatively, a conventional high-frequency coaxial resonator 36 shown in FIG. 10 comprises a tubular dielectric member 38 having a through hole 37 and inner and outer conductors 39 and 40 which are provided on inner and outer peripheral surfaces of the tubular dielectric member 38, respectively, so as to define a high-frequency coaxial resonator of a half wave type.
Each of these high-frequency coaxial resonators 30 and 36 is equivalent to an LC parallel resonance circuit. In use, the inner conductor 33 or 39 is connected to a signal-carrying pattern on a circuit board through a central conductor (not shown) which is inserted in the through hole 31 or 37 while the outer conductor 34 or 40 is connected to a ground point provided on the circuit board.
In the high-frequency coaxial resonators 30 and 36 having the aforementioned structures, however, one or both end surfaces are open-ended, thereby exposing the dielectric members 32 and 38, and hence unwanted interference can take place between the open-ended surfaces and external circuits if said external circuits are provided in proximity to the high-frequency coaxial resonators 30 and 36. Therefore, the high-frequency coaxial resonators 30 and 36 must appropriately be spaced apart from external circuits, which thereby hinders in high-density packaging of circuit boards.
Furthermore, since the resonant frequencies of respective sampler of the high-frequency coaxial resonators 30 and 36 having the aforementioned structures are dispersed during the manufacturing steps, the tubular dielectric members 32 and 38 are initially prepared in excess of the prescribed lengths, so that the resonant frequencies thereof are lower than prescribed values, and thereafter are reduced in length by polishing the end surfaces thereof or the like, to increase the resonance frequencies to prescribed values. Thus, the procedure for adjusting the resonant frequencies is extremely complicated.